How Many Inboxes Per Domain for Cold Email? A Strategy

A laptop displaying a cold email strategy for the optimal number of inboxes per domain.

You’ve spent hours researching prospects, writing personalized copy, and setting up your campaign. You hit "send" and wait, only to find your open rates are abysmal and your domain is getting flagged. The problem often isn’t your message; it’s your technical setup. A common and costly mistake comes down to a simple question: how many inboxes per domain for cold email are you using? Loading up one domain with a dozen or more inboxes is one of the fastest ways to destroy your sender reputation before you even get started. Let's walk through why this approach backfires and how to build a resilient infrastructure instead.

Key Takeaways

Prioritize Domain Health Over Inbox Quantity: To maintain a strong sender reputation, limit each domain to 2-6 inboxes. The correct way to increase your sending volume is by strategically adding more domains, not by overloading a single one with too many mailboxes.
Build Trust Before You Send a Single Email: A proper warm-up process is non-negotiable for new inboxes. Gradually increase your sending volume over several weeks and focus on generating real engagement to prove to email providers that you're a legitimate sender.
Treat Your Setup Like a System, Not a Task: Effective cold email requires ongoing management. Distribute your sending across multiple domains, dedicate inboxes to specific campaigns, and consistently monitor performance metrics to catch issues before they damage your reputation.

How Many Inboxes Should You Use Per Domain?

When you're setting up for cold email, figuring out the right number of inboxes per domain is crucial for your deliverability. Let's get straight to the point: less is more. The goal is to look like a legitimate business, not a spam operation, and that means keeping your setup clean and focused.

The general consensus among outreach experts points to a "sweet spot" of about 2 to 6 mailboxes per domain. This range gives you enough sending capacity to make an impact without putting your domain's reputation at risk. Think of it as the perfect balance between scaling your efforts and flying under the radar of spam filters. Sticking to this number helps you maintain a healthy sender reputation, which is the foundation of any successful cold email strategy.

If you're looking to send at a higher volume, your first thought might be to just add more inboxes. A better approach is to scale your cold email campaigns by using multiple domains. Instead of loading up one domain with 10 or 20 inboxes, you would use five domains with 2 to 3 inboxes each. This strategy distributes your sending volume, minimizes risk if one domain runs into trouble, and ultimately leads to more replies. While some might try to push the limits, a common guideline is to avoid high-density setups. It’s a risky move that can quickly damage your deliverability across the board.

Why Fewer Inboxes Per Domain Is Better for Deliverability

When you're setting up your cold email strategy, it’s tempting to think that more is better. More inboxes, more emails, more leads, right? Not exactly. In the world of email deliverability, the "less is more" approach often wins. Spreading your sending activity across a smaller, more manageable number of inboxes per domain is one of the smartest moves you can make for your campaign's long-term health. It’s all about building a sustainable system that email providers trust.

Think of it this way: each domain you own has a reputation to uphold. Bombarding recipients with high volumes of email from dozens of inboxes tied to a single domain looks suspicious to providers like Google and Microsoft. It’s a pattern they associate with spammers. By limiting the number of inboxes per domain, you can warm them up properly, control your sending volume, and fly under the radar of aggressive spam filters. This careful approach protects your domain’s reputation, keeps you out of the spam folder, and ultimately ensures your messages actually get seen by the people you want to reach.

Protect Your Domain Reputation

Your domain reputation is everything in cold email. It’s like a credit score that tells email providers whether you’re a trustworthy sender. Sending too many emails too quickly from one domain is a huge red flag that can damage this score. When providers see a massive volume of mail coming from a single source, their spam filters kick in, and your deliverability plummets. The primary goal is to protect your domain's reputation, because once it’s tarnished, it’s incredibly difficult to repair. A bad reputation affects every single inbox associated with that domain, grinding your outreach efforts to a halt. By using fewer inboxes, you can maintain a natural, steady sending pace that builds trust with providers instead of eroding it.

Avoid Scrutiny from Email Providers

Email providers are constantly on the lookout for activity that signals spam. One of the easiest ways to attract unwanted attention is by setting up an unusually high number of inboxes on one domain. While there's no magic number, most experts agree that keeping it between two and six inboxes per domain is a safe bet. Anything more than that can look like you're trying to game the system. This is why a strategy involving hundreds of mailboxes on a single domain is so risky—it’s an immediate red flag. Your goal is to look like a legitimate business conducting thoughtful outreach, not a bulk sender blasting out emails. A smaller number of inboxes helps you maintain that low profile.

Stay Out of the Spam Folder

Ultimately, the goal of any email campaign is to land in the primary inbox. The speed and volume of your sending have a direct impact on whether that happens. If you send too many emails and a portion of recipients mark them as spam, your domain’s reputation takes a serious hit. This makes it even harder for future emails to avoid the spam folder. Limiting your inboxes per domain helps you naturally control your sending volume and velocity. This reduces the chances of overwhelming recipients and triggering spam complaints. A slow, steady, and deliberate approach is your best defense against the spam folder and is a core principle of a strong cold email strategy.

The Risks of Using Too Many Inboxes on One Domain

It might seem logical that more inboxes on a single domain would let you send more emails, but this approach can seriously backfire. Loading up one domain with dozens of inboxes is a fast track to damaging your sender reputation. Email service providers (ESPs) like Google and Microsoft are incredibly sophisticated; they monitor sending patterns closely, and a sudden flood of activity from one domain looks suspicious. Instead of increasing your reach, you risk getting your entire operation shut down before it even gets going. Let's break down the specific risks you face.

Getting Flagged as Spam

One of the biggest mistakes you can make is sending too many emails too quickly from a new domain. This behavior is a massive red flag for spam filters. When an ESP sees a single domain suddenly activate 20 inboxes and start sending hundreds of emails, it assumes the worst—that you're a spammer. Even if your emails are perfectly crafted, the sheer volume and velocity of your sends will trigger automated defenses. This means your messages get routed directly to the spam folder, where they'll never be seen by your prospects.

Landing on a Blacklist

If your sending behavior is aggressive enough, you won’t just get flagged as spam—your entire domain could end up on a blacklist. A blacklist is a real-time database that identifies domains and IP addresses believed to be sending spam. Once you’re on one, it’s incredibly difficult to get off. The main goal of any cold email strategy should be to protect your domain's reputation. Getting blacklisted doesn't just affect one inbox; it taints every single email account associated with that domain, making it nearly impossible for any of your messages to reach their destination.

Lowering Your Deliverability Rate

Every time an email lands in spam or a recipient marks your message as junk, it chips away at your domain’s reputation. This directly impacts your email deliverability, which is the measure of how many of your emails actually make it to the inbox. If too many people mark your emails as spam, ESPs take note and start treating all messages from your domain with suspicion. Soon, even your best-performing campaigns will see a drop in engagement because fewer people are receiving them. It creates a downward spiral that’s hard to recover from.

Facing Sending Limits and Throttling

When ESPs detect suspicious activity, they don’t always block you outright. Sometimes, they’ll start throttling your messages, which means they deliberately slow down or limit the number of emails you can send. This is their way of protecting their users from what they perceive as a potential spam attack. For cold outreach, it's a good practice to limit each mailbox to around 30–50 emails per day to stay under the radar. Trying to push past these unwritten rules by adding more inboxes will only lead to throttling and diminishing returns on your campaigns.

How to Warm Up New Inboxes for Cold Email

Before you send a single cold email from a new inbox, you need to warm it up. Think of it like meeting a new group of people—you wouldn’t walk in and immediately start shouting your sales pitch. Instead, you’d introduce yourself and build a little rapport first. Warming up your inbox is the digital equivalent of that. It’s the process of building a positive sender reputation with email service providers (ESPs) like Google and Microsoft by showing them you’re a legitimate, trustworthy sender, not a spammer.

This isn’t a step you can skip. A brand-new inbox that suddenly starts sending hundreds of emails a day is a massive red flag for spam filters. By gradually increasing your sending activity and generating positive engagement, you teach the algorithms that your emails are wanted. This process involves a few key steps: slowly ramping up your sending volume, getting real people to interact with your emails, and making sure your technical setup is solid. A proper warm-up is the foundation of any successful cold email strategy and is essential for keeping your messages out of the spam folder and in front of your prospects.

Increase Sending Volume Gradually

The golden rule of warming up an inbox is to start low and go slow. Firing off hundreds of emails on day one is the fastest way to get your domain flagged. Instead, you want to mimic the behavior of a real person who is just starting to use their new email account. This means beginning with a very small number of emails and increasing that volume incrementally over several weeks.

For example, you might start by sending 5-10 emails on the first day, then 15-20 the next, and so on. This gradual increase demonstrates to ESPs that your sending activity is natural and not automated spam. This slow ramp-up period is crucial for establishing a good sender reputation, which directly impacts your ability to land in the primary inbox. Rushing this process will only hurt your deliverability in the long run, so patience is key.

Build Real Engagement

Sending emails is only half the battle; getting positive interactions is what really builds trust with email providers. During the warm-up phase, your goal is to generate as much positive engagement as possible. This means getting opens, clicks, and, most importantly, replies. These actions signal to ESPs that recipients actually want to receive your emails.

A great way to do this is by sending your warm-up emails to a list of "friendly" inboxes—think colleagues, friends, or other accounts you control. Ask them to open your emails, click any links, and reply to your message. It’s also critical to send emails only to valid addresses. Using an email verification tool helps you avoid bounces, which are negative signals that can damage your reputation before you even get started.

Set Up Your Authentication Protocols

Before you even think about your sending schedule, you need to handle the technical setup. Email authentication protocols like SPF, DKIM, and DMARC are non-negotiable. Think of them as your domain's digital passport—they prove to receiving mail servers that you are who you say you are and that your emails are legitimate.

SPF (Sender Policy Framework) specifies which mail servers are authorized to send email on behalf of your domain.
DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, verifying that the message wasn't altered in transit.
DMARC (Domain-based Message Authentication, Reporting & Conformance) tells servers what to do with emails that fail SPF or DKIM checks.

Setting these up correctly is a foundational step that prevents spoofing and significantly improves your email deliverability.

Plan Your Warm-Up Timeline

A successful warm-up doesn't happen by accident; it requires a structured plan. You should map out a clear timeline, typically lasting anywhere from two to four weeks, depending on your desired daily sending volume. This plan should detail how many emails you’ll send each day and how you’ll gradually increase that number. Consistency is crucial here—avoid erratic sending patterns, like sending 20 emails one day and then 150 the next.

Your timeline should incorporate all the elements we've discussed: a gradual sending ramp, a strategy for generating engagement, and the initial technical setup. While automated warm-up tools can manage the day-to-day process, understanding the strategy behind it is vital. This deliberate approach ensures you build a strong, positive sender reputation that will support your cold outreach campaigns for the long haul.

Common Myths About Inbox Quantity

When it comes to cold email, it’s easy to get caught up in advice that sounds good on the surface but can actually harm your campaigns. The number of inboxes you use is a perfect example. Let's clear up some of the most common myths so you can build a strategy that protects your domain and gets your emails delivered.

Myth: More Inboxes Equal Better Deliverability

You might think that spreading your sending volume across dozens of inboxes on a single domain is a clever way to fly under the radar. The reality is quite the opposite. Loading up one domain with a high number of mailboxes is a huge red flag for email service providers.

Most deliverability experts recommend keeping the number of mailboxes per domain low, typically between two and six. Anything more than that looks suspicious and can seriously damage your email deliverability. Instead of helping you send more, this approach makes it more likely that all your inboxes will land in the spam folder.

Myth: Volume Is More Important Than Quality

The old "spray and pray" approach is a relic of the past. Sending a massive volume of emails won't get you results if they never reach the inbox. Success in cold email hinges on quality, not quantity. This means focusing on a clean, verified email list and writing personalized messages that resonate with your recipients.

Think about it from the provider's perspective: a sudden, high-volume blast of generic emails looks exactly like spam. Prioritizing a well-maintained list and thoughtful outreach will always outperform a high-volume strategy with a poor-quality foundation. Following the rules and focusing on genuine engagement is the only sustainable way to run cold email campaigns.

Misunderstanding How Sender Reputation Works

At the heart of all these myths is a misunderstanding of sender reputation. Your domain's reputation is your most valuable asset in cold emailing. Every action you take either builds or erodes it. Sending too many emails from one domain or mailbox too quickly signals to providers like Google and Microsoft that you might be a spammer.

Once your reputation is damaged, your emails are far more likely to be filtered into spam or blocked entirely. The main goal is to protect your domain’s health at all costs. This is why maintaining sender reputation is such a challenge when scaling campaigns—it requires a careful, strategic approach to volume, cadence, and infrastructure.

How to Strategically Manage Multiple Domains and Inboxes

Once you understand the right number of inboxes to use per domain, the next step is building a smart, sustainable system for managing them. A well-organized strategy is what separates campaigns that get results from those that get blacklisted. It’s not just about sending emails; it’s about creating a resilient infrastructure that protects your reputation and supports your growth. This involves spreading your sending activity, dedicating inboxes to specific goals, and establishing a solid routine for monitoring everything. Let’s walk through how to put these pieces together.

Distribute Your Sending Volume Across Domains

Think of your domain reputation like a credit score—you want to build it carefully and protect it. Putting too much sending activity on a single domain is risky. Instead, spread your total email volume across multiple domains. This approach minimizes the risk associated with any single domain and helps maintain a healthy sending reputation overall. For example, rather than using ten inboxes on one domain, it's much safer to use two inboxes each across five different domains. This distribution makes your sending patterns look more natural to email providers and reduces the chance of any one domain getting flagged, which could halt your outreach entirely. It’s a simple way to build a more robust sending infrastructure.

Allocate Inboxes for Specific Campaigns

To keep your outreach organized and effective, assign specific inboxes to different campaigns. For instance, you could use one set of inboxes for targeting enterprise clients in the tech industry and another set for reaching out to small businesses in retail. This segmentation does more than just keep you organized—it allows you to tailor your messaging and closely track the performance of each campaign. When you know exactly which inbox is tied to which outreach effort, you can easily identify what’s working and what isn’t. This makes it much simpler to optimize your strategy, improve reply rates, and scale your most successful campaigns without disrupting others.

Create a Workflow for Monitoring and Maintenance

A "set it and forget it" approach doesn't work for cold email. You need a consistent workflow for monitoring your domains and inboxes. Sending too many emails too quickly is one of the fastest ways to get flagged as spam, so a patient, steady approach is essential. Your workflow should include regularly checking key metrics like open rates, reply rates, and bounce rates for each inbox. This helps you spot problems before they escalate. Using a dedicated platform can streamline this process by automating DNS setup and providing a clear view of your performance, making it easier to manage multiple mailboxes efficiently. If you need help building a reliable system, you can always book a call to discuss your infrastructure.

Key Metrics for Tracking Inbox Performance

Sending cold emails without tracking your performance is like driving with your eyes closed. You might be moving, but you have no idea if you're headed in the right direction. Paying close attention to a few key numbers will tell you exactly what’s working, what’s not, and when you need to adjust your strategy to protect your domain.

Essential Deliverability Indicators

These are the foundational metrics that tell you if your emails are successfully reaching their destination. Think of them as your technical health check. A sudden drop here is the first sign of trouble. Keep a close eye on your spam complaint rate, which should always stay below 0.1%. If it creeps up, you’re in the danger zone. Similarly, you should aim for a bounce rate of 2% or less, as a higher number suggests your list quality is poor. Remember that sending too many emails too soon is one of the fastest ways to get flagged. Patience and a steady, gradual approach are essential for long-term success.

Important Engagement Metrics

Once your emails land in the inbox, you need to know if anyone is actually reading them. While the average cold email open rate is around 27.7%, the most important metric is your reply rate. This is where personalization makes all the difference; emails that are genuinely personalized get two to three times more replies. Don’t forget the follow-up, either. Sending a second or third message can increase your reply rates by more than 50%, yet nearly half of all salespeople never send a single follow-up. That’s a huge missed opportunity you can easily capitalize on.

Red Flags to Watch For

Sometimes, email providers will give you subtle warnings before they drop the hammer. One of the most common is throttling, where providers start to limit or block your messages due to suspicious activity. This often happens when you try to scale your campaigns too quickly. The underlying issue is almost always your sender reputation. The real challenge is maintaining sender reputation across multiple domains as you increase your volume. If you notice your deliverability score dropping, especially while managing several inboxes, it’s a clear signal that you need to investigate your setup and strategy immediately.

Your Technical Checklist for Optimal Inbox Management

Let's talk about the technical side of things. I know, the acronyms and settings can feel a bit daunting, but getting your technical setup right is the foundation of any successful cold email strategy. Think of it like building a house—you need a solid foundation before you can even think about decorating. The same goes for your email outreach. Skipping these steps is a fast track to the spam folder, and all your hard work writing great emails will go to waste.

This checklist covers the non-negotiables for managing your inboxes effectively. We'll walk through the essential configurations and protocols that signal to email providers like Google and Microsoft that you're a legitimate sender. Properly configuring your setup from the start protects your domain reputation and ensures your messages actually land in front of your prospects. It’s a crucial step that pays off in the long run with better deliverability and more consistent results. A dedicated email infrastructure handles much of this for you, but it's still important to understand what's happening behind the scenes.

Essential DNS Configurations

Your Domain Name System (DNS) records are like your domain's digital ID card. They help mail servers verify that your emails are actually coming from you. Getting these settings right is critical for building trust with providers. For cold email, this often involves setting up a dedicated IP address, which keeps your sender reputation isolated from others. While you can do this manually, using a platform that automates the DNS setup process can save you a ton of time and prevent costly errors. This ensures your foundation is solid from day one, giving your emails the best possible chance of reaching the inbox.

Must-Have Authentication Protocols (SPF, DKIM, DMARC)

Think of SPF, DKIM, and DMARC as a three-part security check for your emails. SPF (Sender Policy Framework) lists the servers authorized to send email from your domain. DKIM (DomainKeys Identified Mail) adds a digital signature to your emails to prove they haven't been tampered with. DMARC (Domain-based Message Authentication, Reporting & Conformance) then tells receiving servers what to do with emails that fail SPF or DKIM checks. Implementing all three is non-negotiable. They work together to authenticate your emails, protect your domain from being spoofed, and significantly improve your deliverability.

Planning Your Sending Infrastructure

When you're scaling your outreach, it’s tempting to send as many emails as possible from one inbox, but that’s a recipe for trouble. A smart sending infrastructure limits each mailbox to around 30-50 emails per day. This slow-and-steady approach helps you fly under the radar of spam filters and avoid throttling issues from email providers. As you add more domains and inboxes, the main challenge becomes maintaining a good sender reputation across all of them. Careful planning and consistent monitoring are key to scaling your volume without sacrificing your deliverability rate. This is where having a system to manage inboxes at scale becomes incredibly valuable.

How ScaledMail Helps You Manage Inboxes at Scale

Managing multiple inboxes for cold outreach can quickly become a full-time job of technical tweaks and performance tracking. The more you scale, the more complex it gets. This is precisely the problem we built ScaledMail to solve. Our platform is designed to handle the heavy lifting of inbox management, so you can focus on writing great emails and connecting with prospects. We provide the infrastructure and automation that lets you scale your outreach confidently without compromising your deliverability.

The Benefit of a Dedicated Infrastructure

When you send emails from a standard provider, you’re often sharing resources with thousands of other users. If one of them gets flagged for spam, your reputation can take a hit, too. A dedicated infrastructure gives you your own private lane on the email highway. ScaledMail provides custom-built systems with dedicated IP addresses, so your sender reputation is entirely in your hands. We handle the complex DNS setup for you, ensuring every technical detail is configured for optimal performance from day one. This means your inboxes are isolated from bad actors and primed for high deliverability.

Automated Warm-Up and Maintenance

Manually warming up a handful of inboxes is tedious. Warming up dozens or hundreds is nearly impossible to do correctly. This is where automation becomes a lifesaver. Instead of slowly sending emails back and forth yourself, our system handles the entire warm-up process for you. We gradually increase sending volume and simulate real, positive engagement to build a strong reputation with email providers like Google and Microsoft. This ensures your inboxes are seen as credible sources, which is essential for keeping your cold emails out of the spam folder and in front of your prospects.

Advanced Performance Monitoring

Sending emails without tracking performance is like driving with your eyes closed. You need clear data to understand what’s working. While basic open and reply rates are helpful, true inbox management requires deeper insights. Our platform provides detailed analytics on deliverability trends, bounce rates, and overall inbox health. You can quickly see which inboxes are performing well and which might need attention, allowing you to make data-driven decisions to protect your domain reputation. This level of monitoring helps you optimize your outreach strategy and ensure your campaigns are always running at peak efficiency.

Cold Email Mistakes That Hurt Your Domain

Even the most carefully crafted cold email campaign can fail if it’s undermined by technical missteps. These mistakes often fly under the radar, but they can do serious damage to your domain reputation, making it nearly impossible to reach the inbox. The good news is that they are entirely preventable. By understanding what email service providers look for, you can avoid the common traps that get senders flagged as spam.

Protecting your domain is the foundation of any successful outreach strategy. It’s about playing the long game and building a history of positive sending behavior. Let’s walk through three of the most critical mistakes we see people make and cover the simple adjustments you can implement to keep your deliverability high and your campaigns running smoothly. Think of this as your essential checklist for maintaining a healthy sending infrastructure.

Putting Too Many Inboxes on One Domain

When you want to scale your outreach, it’s tempting to think that more inboxes on a single domain will get you there faster. In reality, this approach often backfires. Loading up one domain with dozens of inboxes is a huge red flag for email providers like Google and Microsoft. They see this as unnatural behavior and are more likely to scrutinize your activity, which can lead to deliverability problems across all your accounts.

Instead, a more sustainable strategy is to spread your sending volume across multiple domains. While there's no magic number, many experts suggest keeping the number of mailboxes per domain low, typically between two and six. This approach looks more organic to email providers and insulates your operation. If one domain runs into an issue, the others aren't affected, protecting your overall outreach efforts.

Skipping the Warm-Up Process

Sending a high volume of emails from a brand-new inbox is one of the quickest ways to land in the spam folder. Email providers are naturally suspicious of new accounts that immediately start blasting out messages. You need to build a positive sending history first, and that’s exactly what the warm-up process is for. It involves gradually increasing your sending volume over several weeks.

This process mimics the behavior of a real person, building trust with providers like Gmail and Outlook. A proper email warm-up involves sending and receiving emails, getting replies, and having your messages marked as important. It signals that you're a legitimate sender, not a spammer. Skipping this step is a critical error that tells providers you can't be trusted, making it incredibly difficult to reach anyone's inbox.

Ignoring Performance Metrics

Sending cold emails without tracking your performance is like trying to find a destination without a map. You have no idea what’s working, what’s failing, or why. Ignoring key metrics like open rates, bounce rates, and reply rates means you’re missing crucial feedback that could save your domain from being blacklisted. A sudden spike in bounce rates, for example, is a clear warning sign that something is wrong with your list or your sending practices.

Using a cold email tool with robust analytics is essential for monitoring the health of your campaigns. These platforms help you understand which messages resonate and which ones are causing deliverability issues. With advanced performance monitoring, you can catch problems early and make data-driven adjustments to protect your sender reputation. Consistently reviewing your metrics ensures you can refine your approach and maintain strong deliverability over the long term.

Frequently Asked Questions

I need to send a lot of emails. Can I just add more inboxes to my main domain? That’s a common first thought, but it’s one of the riskiest things you can do for your domain’s health. Loading up a single domain with ten, twenty, or more inboxes looks highly unnatural to email providers and is a huge red flag for their spam filters. The much safer and more effective way to scale your sending volume is to add more domains, not more inboxes. Stick to the sweet spot of 2 to 6 inboxes per domain, and if you need more capacity, simply acquire another domain and repeat the process. This distributes your sending activity and protects your entire operation if one domain runs into trouble.

How long should I warm up a new inbox before using it for a real campaign? Patience is everything here. You should plan for a warm-up period of at least two to four weeks before you start sending any real campaigns from a new inbox. This process isn't just a formality; it's how you build a positive sending history and prove to providers like Google and Microsoft that you're a legitimate user, not a spammer. Rushing this step by sending too many emails too soon is the fastest way to get your new inboxes flagged and ruin their deliverability before you even get started.

Should I use my main company domain for cold outreach? Absolutely not. You should always protect your primary business domain at all costs. Cold outreach, even when done perfectly, carries inherent risks to your sender reputation. You don't want a campaign issue to prevent your regular business emails—like those to current clients, partners, or your own team—from being delivered. The best practice is to purchase secondary domains that are similar to your main one (e.g., getcompany.com instead of company.com) and use those exclusively for your outreach efforts.

What's the most important metric to watch to know if my inboxes are healthy? While it’s easy to get focused on open and reply rates, the true health of your inboxes is reflected in your technical deliverability metrics. Pay close attention to your bounce rate and spam complaint rate. Your bounce rate should always be under 2%, and your spam complaints should be below 0.1%. If you see these numbers start to creep up, it’s the earliest warning sign that your domain reputation is taking a hit, long before you see a major drop in your engagement numbers.

My open rates just dropped. What's the first thing I should check? A sudden drop in open rates usually points to a deliverability problem, meaning your emails are likely landing in the spam folder. The first thing to do is a technical check-up. Make sure your authentication protocols—SPF, DKIM, and DMARC—are correctly set up and validated. Then, use a free tool to see if your domain has landed on any blacklists. If your technicals are solid, the issue is likely related to your sending behavior, such as a poor-quality email list causing high bounces or a sudden increase in sending volume that triggered spam filters.